Technical Field
The present disclosure relates to a wireless power transmission system, a power transmitting device and a power receiving device.
Background
Japanese Laid-Open Patent Publication No. H8-340285 discloses a wireless electric power transmission apparatus that uses electromagnetic induction to transmit electric power between two non-contact electric circuits.
The Journal of The Institute of Electrical Engineers of Japan Vol. 129 (2009), No. 7, pages 414-417 discloses a wireless electric power transmission apparatus that uses magnetic field resonance and electric field resonance to transmit electric power between two non-contact electric circuits.
With the technique disclosed in Japanese Laid-Open Patent Publication No. H8-340285, due to a large electric power loss in a coil for transmitting electric power, there is a disadvantage that electric power cannot be transmitted efficiently. Further, with the technique disclosed in Japanese Laid-Open Patent Publication No. H8-340285, referring to the description such as paragraph (0058) of such document, a distance across which electric power can be transmitted is limited within a range in a millimeter order to a centimeter order, and thus there are limited applications.
With the technique using magnetic field resonance disclosed in The Journal of The Institute of Electrical Engineers of Japan Vol. 129 (2009), No. 7, pages 414-417, although a distance through which electric power can be transmitted can be extended to an order of tens of centimeters to a meter order, it is necessary use a coil, which is obtained by winding a conductor, to produce a magnetic field to obtain resonance. When transmitting electric power, since it is necessary to let an electric current flow through this coil, a conductor loss cannot be avoided. Further, since the conductor used for the coil is generally a metal wire rod, there will be an increase in the mass of the power transmission/reception apparatus incorporating such a coil.
Further, with the technique using electric field resonance disclosed in The Journal of The Institute of Electrical Engineers of Japan Vol. 129 (2009), No. 7, pages 414-417, instead of a magnetic field, an electric field is used for resonance. According to such a technique, although a coil is not used in resonance, an electric length at which resonance is obtained needs to be obtained by a conductor line. Thus, electrodes for electric field coupling needs to be used that are conductor lines having a length of a quarter-wavelength symmetrically disposed in a meandering manner from a power feeding point and a power receiving point, respectively. Therefore, for example, when a resonance frequency is low, a conductor line length of the electrode for obtaining resonance becomes longer. Also, an alternating current resistance due to interference between spatially adjacent electrically-conductive lines, namely, due to the coupling between the wires causes a conductor loss in a similar manner as the magnetic field resonance, and transmission efficiency of the electric power decreases. Particularly, as a gap between electrically conductive lines of the electrodes for electric field coupling is narrowed to reduce an electrode size, the alternating current resistance due to the coupling between wires increases.